Seismic activity grew in central Oklahoma in the 18 months leading up to Dec. 31, 2015, but declined markedly during the following year as the state began to regulate oil and gas wastewater disposal more aggressively, the US Department of Energy’s Fossil Energy Office (FEO) reported. Decreased oil and gas production in response to falling prices also played a part, it added.
FEO’s National Energy Technology Laboratory, the University of Oklahoma, and the Oklahoma Geological Survey (OGS) jointly studied seismic events in the Sooner State, where earthquakes grew markedly from the 1980s through 2008. The final report, which the OGS released on June 6, found that more than 95% of the quakes in 2015 occurred in two main regions representing about 17% of Oklahoma’s total land area:
• A central zone east of the major Nemaha Fault comprising parts of nine counties mostly north of Oklahoma City and west of Tulsa.
• A northwestern zone west of the same fault, comprising parts of six counties.
Oil and gas wastewater disposal in the two regions increased considerably from July 1, 2014, to Dec. 31, 2015, as the number of seismic events grew, researchers found. Earthquakes with magnitudes greater than 3.0 rose from 579 in 2014 to 903 in 2015, then decreased to 623 in 2016, they reported.
The reduction in seismic events correlated to decreased wastewater injection, partly due to Oklahoma Corporation Commission regulatory actions and partly because oil and gas production declined from 2015 to 2016 in response to falling prices, the study said.
Using a denser network of seismometers and high-resolution gravity and magnetic measurements, researchers could detect and locate more precisely all 2.0 magnitude or greater earthquakes in Oklahoma, FEO said. Accurate locations are critical, since 50% of the earthquakes that occur in Oklahoma are on faults that were not identified previously, including one that the team discovered near Cushing.
The researchers also applied a novel simulation approach to characterize the geologic variability around an injection well and used it to estimate the pressure increase on a fault in the basement rock that could trigger seismic events, FEO said. Such an approach can be used to help identify safe injection rates and safe distances from injection wells to faults, it said.
Based on its findings, the team met with staff members from the OCC’s Oil & Gas Conservation Division to review the seismic events and wastewater injection data, and with staff from the Kansas Corporation Commission and the Kansas Geological Survey to discuss data and approaches to regulation, FEO said.
The study team also conducted public outreach to address concerns about induced seismicity. It made presentations to the Federal Emergency Management Agency, local and state emergency management groups, and civic organizations. The outreach also included a strong online presence; active engagement and open dialogue within the academic community; media interviews and statements; and the production of preparedness materials, FEO said.
Contact Nick Snow at [email protected].